This study was conducted to determine infestation levels of southern green stink bug, Nezara viridula (L.), and green stink bug, Acrosternum hilare (Say), on host plants including corn, cotton, soybean, sorghum, and non-crop vegetation in a multicrop ecosystem. Stink bug infestations responsible for crop damage on vegetative and panicle stages of grain sorghum planted on different dates were also investigated. Both N. viridula and A. hilare appeared to establish a first generation on non-crop grasses surrounding cultivated fields and then moved to soybean or cotton to begin a second generation. These stink bugs did not appear to be attracted to corn or sorghum when cotton and soybean were in attractive growth stages in the same ecosystem in this study. A large population of N. viridula infested soybean during R5 (beginning seed) to R7 (beginning seed maturity) plant growth stages. Sorghum planted in May was not infested with stink bugs, whereas sorghum planted in mid- to late June or early to mid-July was infested with a large numbers of N. viridula, but not A. hilare. Movement of N. viridula from soybean to sorghum coincided with attractive reproductive stages of sorghum. Southern green stink bugs caused significant damage to sorghum when panicles were caged and infested from milk stage to seed maturity or from soft-dough stage to seed maturity with 4 adults or 10 nymphs per panicle. No reductions in seed weight or seed germination were found when 5 adults were confined on sorghum panicles during hard-dough to seed maturity. These data would suggest that economic thresholds for N. viridula under conditions of this study were 3 adults or 6 to 9 nymphs per panicle for sorghum in milk stage to seed maturity. The reductions in seed weight and seed germination were associated with the number of stink bugs per panicle and the stage of seed development.

Stink bugs are major pests of agricultural crops throughout Virginia and much of the United States. Knowledge of the biology, the species complex, and insecticide susceptibility can improve management. A survey was conducted in Virginia to determine the species complex in soybean and cotton and to monitor for nonnative species. Seven stink bug species were identified. Acrosternum hilare (Say) and Euschistus servus (Say) were the most common. Two sampling methods, the sweep net and the beat sheet, were assessed in soybean and cotton. There was less variability with the sweep net method compared to the beat sheet method. Laboratory bioassays and field trials were conducted to evaluate the toxicity and efficacy of selected conventional and organic insecticides against A. hilare and E. servus. In bioassays with conventional insecticides, A. hilare adults and nymphs were susceptible to all pyrethroids tested. Generally, the neonicotinoids, dinotefuran and clothianidin, were more toxic to A. hilare, while thiamethoxam and acetamiprid were more toxic to E. servus. In soybean field efficacy trials, dinotefuran performed comparably to the organophosphates and pyrethroids. Laboratory bioassays with organic insecticides resulted in moderate to high levels of mortality, and in antifeedant and repellency responses. Likewise, soybean field trials indicated that a single application can reduce stink bug numbers for up to two days after treatment; however in tomato field trials multiple weekly applications did not result in significant reductions in stink bug damage. A weather model to predict abundance of A. hilare adults was developed using weekly black light trap catch data collected from 1990 to 2007 at a single location. The two weather variables that resulted in a significant model were days below freezing and mean monthly precipitation from January to April. The model was validated by correlating five independent data sets to predicted weekly trap catch. Mean trap catch plotted over time showed three peaks. In accordance with A. hilare developmental rates, the peaks indicated that two generations and a partial third occur in Virginia. Cumulative trap catch estimated from the 18-yr trap catch mean showed that 10, 50, and 90% of the total seasonal catch should occur by 153, 501, and 1066 degree days, respectively. / Ph. D.

Cage studies were performed to determine if the current thresholds for stink bugs in soybean (one bug per 0.3 row m) need to be adjusted based on current soybean production practices and species present. Several soybean development stages were infested by two native stink bug species for three weeks using small cages in a field of double crop soybean at sites in Virginia, Maryland, and Delaware during 2007-2009. Large field cages were infested by an introduced species for two weeks in 2010-2011. Results showed that Euschistus servus Say and Acrosternum hilare Say adults or nymphs did not cause different levels of injury to soybean seed quality or effects on yield. Both A. hilare and the introduced Halyomorpha halys Stål injured soybean seed in a similar fashion at threshold-level densities. Full flowering R2 stage soybean were least affected by stink bug feeding, and full pod and beginning seed R4-R5 stage soybean were slightly more sensitive to injury than R6 although not at the Maryland 2011 site. Several sites had increased seed injury and decreased yield at threshold density populations. Finally, visual observations of stink bug vertical distribution inside soybean canopies were taken several times per day and compared with ambient and within-canopy temperature and relative humidity. Results indicated that these conditions did not influence the percentage of stink bugs below the top 38 cm sweep net intercept zone. In both years of observations, between 15 and 20% of stink bugs were observed below the 38 cm sweep net zone. / Master of Science in Life Sciences